The present invention relates to blind fasteners for securing workpieces of a crushable or composite material and more particularly to a blind fastener providing a blind head with a large effective bearing surface on the blind side of such workpieces.
In certain applications, especially those involving workpieces of crushable or composite materials, it is desirable to utilize a blind fastener providing a large bearing area under the blind head. The large bearing or surface area around the workpiece opening on the blind side assists in inhibiting localized crushing and flaking of the workpiece material engaged by the blind head.
Fasteners generally of the type of the present invention are shown in U.S. Pat. No. 3,345,900 to J. P. Villo issued Oct. 10, 1966, U.S. Pat. No. 4,033,222 to L. B. Wilson, issued July 5, 1977, U.S. Pat. No. 4,168,650 to W. F. Dahl, et al, issued Sept. 25, 1979, U.S. Pat. No. 4,457,652 to J. D. Pratt, issued July 3, 1984 and U.S. Pat. No. 4,203,346 to D. E. Hall et al, issued May 20, 1980.
The preceding patents generally disclose a multipiece fastener including a main sleeve and an expandable sleeve which forms a blind head as it is axially moved by a pin member over the blind end of the main sleeve. The '900 patent to Villo generally shows this structure but does not form a blind head having a large bearing area or "footprint". The '222 patent to Wilson shows a structure including three expandable sleeves in an effort to provide a blind head having a large bearing area. The '650 patent to Dahl et al and '652 patent to Pratt show an expandable sleeve having a reduced section portion at the leading end which bulbs radially outwardly to ostensibly provide a large bearing area. A variation of these structures is shown in the '346 patent to Hall et al where the reduced section portion engages a shoulder on the pin member.
The latter set of patents, i.e. Dahl et al, Pratt, and Hall et al, rely upon buckling of the reduced section portion to form the enlarged head. However, it has been determined that such fasteners do not regularly provide a blind head which engages the adjacent workpiece surface over a significant portion of the available surface area of the blind head. Thus, while the reduced section portion will in fact bulb radially outwardly to form an enlarged head, the surface at the radially outer end of the bulbed head tends to move axially away from the workpiece surface and hence does not provide the desired engagement with the workpiece surface over the full radial extent of the bulbed head.
In the present invention it has been found that a large blind side bearing area can be achieved by providing an expandable sleeve structure having a secondary or reduced section portion which is connected to the remainder or primary portion of the sleeve by a frangible section. The fastener will be set by a relative axial force applied between the pin and the main and expandable sleeves whereby the expandable sleeve is moved over a blind end of the main sleeve. In this way the secondary sleeve portion will be radially expanded first and moved axially until its free end engages the blind side of the workpieces As will be seen with the construction of the present invention the secondary sleeve portion will remain integrally connected to the primary sleeve portion until the axial or column load attains a preselected magnitude of the maximum load at which buckling occurs. At this axial load the reduced section or secondary sleeve portion will be severed from the primary sleeve portion at the frangible section. Now the primary sleeve portion will be effective to guide the buckling secondary sleeve portion and move it to a flattened, closed position. In this position the flattened reduced section portion will engage the confronting blind surface of the workpiece over substantially the entire area of the bulbed, blind head.
Thus it is an object of the present invention to provide a blind fastener for fastening workpieces of a crushable or composite material and which provides a blind head having a large bearing area against the adjacent blind side of the workpieces.
It is another object of the present invention to provide a blind fastener of the above described type having a main sleeve and an expandable sleeve with the expandable sleeve having a reduced section or secondary portion at its leading end adapted to be severed from the remainder or primary portion of the expandable sleeve at a preselected axial or column load at which buckling has been initiated with the severed reduced section portion being substantially folded or collapsed to form a blind head with a large bearing area.
It is another general object to provide a new and unique blind fastener constructed to provide a blind, bulbed head having an enlarged bearing area.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.